The present invention relates to copolymeric organopolysiloxanes comprising SiO.sub.2 and to a method for their preparation. More particularly the present invention relates to the preparation of liquid copolymeric organopolysiloxanes comprising SiO.sub.2. In a preferred embodiment the present invention relates to the preparation of liquid copolymeric organopolysiloxanes comprising SiO.sub.2 and bearing silicon-bonded hydroxyl radicals and silicon-bonded hydrogen radicals.
Copolymeric siloxanes comprising SiO.sub.2 have been disclosed by Daudt et al., U.S. Pat. No. 2,676,182 which are prepared by reacting a silica hydrosol having a pH of less than 5 with an organosilane having the formula R.sub.n SiX.sub.4-n or an organosiloxane having the formula R.sub.n SiO.sub.(4-n)/2 wherein R is alkyl, monocyclic aryl or halogenated monocyclic aryl and X is chlorine or alkoxy. The reaction products are said to range from viscous oils to thermoplastic resins. Some of the copolymeric siloxanes of Daudt et al. are preferred starting materials for the process of this invention.
Organopolysiloxane resins containing R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units, along with RHSiO units and/or HSiO.sub.3/2 units, wherein R is a monovalent hydrocarbon group, are disclosed by Flannigan, U.S. Pat. No. 3,722,247. The resins of Flannigan are said to be preparable in any one of a variety of ways; however, cohydrolysis of hydrolyzable silanes and the reaction of hydrolyzable silanes with a silica hydrosol are the only methods disclosed and only brittle, solid resins are disclosed.
Solventless, flowable organopolysiloxane encapsulating fluids comprising SiO.sub.2 are disclosed by Modic, U.S. Pat. No. 3,205,283 which are prepared by heating a homogeneous mixture of an organic solvent solution of a resinous copolymer containing R.sub.3 SiO.sub.1/2 units, wherein R is a monovalent hydrocarbon radical, and SiO.sub.2 units and a liquid silanol chain-stopped diorganopolysiloxane to remove the organic solvent therefrom.
Brady, U.S. Pat. No. 3,627,851 discloses benzene-soluble copolymeric siloxanes consisting of (CH.sub.3).sub.3 SiO.sub.1/2 units, (CH.sub.3).sub.2 HSiO.sub.1/2 units and SiO.sub.2 units which are prepared by modifying the procedure of Daudt et al. noted above to include (CH.sub.3).sub.2 HSiCl or (CH.sub.3).sub.2 HSiOSiH(CH.sub.3).sub.2 as one of the components to react with the acidic silica hydrosol.